Billions of dollars have been spent in solar energy R&D, and tens of thousands of solar energy devices and systems have been built, sold, and installed across the US. All have been inherently so expensive that they have been cost-supported by tax relief schemes or rebates, and all are utterly unable to compete economically with conventional power plants and heat-power systems. The result of these billions of dollars of R&D is that these solar power systems can NOT provide low-cost power to the consumers of this or any other Nation.
This failure of solar power R&D to yield useful systems is precisely because it was conducted as R&D, not as construction of systems from available low-cost heat-power machinery. The excessive cost of all past solar power systems is a direct result of this struggle to develop and employ equipment and systems of advanced high technical performance.